Back to the original post, does anyone know if there is a difference between the "operators Exec for a 1900" and the executive used by engineers and recorded on 7 track mag tape? Would this be of any use? <<< Does that imply that you - or someone you know has such a tape??? anyhow, to answer the question - "it all depends" I've only limited knowledge of the Engineers test programs tho' I think I have some notes somewhere. So some of what follows may not be precisely correct. Most test programs were normally run under operators exec and were stored on a normal program library tape (these were tapes with a search program (#TAPE) at the start and the rest of the programs in any order following.) The engineers (raw machine) test tape would have started with a minimal exec-mode bootstrappable search program at the start (really only a program loader - not a full exec). This would have been followed by the exec-mode test programs which were presumably in a bootstrap format. Our engineers usually ran such basic test programs from paper tape - this may have been because that process relied on less of the system being operational that the process of finding and loading one from MT. Of course, as always!, the system faults that one remembers were not detected by the test programs ... (On the 1905E one time odd things happened with the Limit register - that took some locating; On the Honeywell dual-processor, one of the two processors started giving some wrong results in floating-point - and as it was (almost) SMP this had effectively random results that took some locating) Andy No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.476 / Virus Database: 269.10.1/888 - Release Date: 06/07/2007 06:36